Water-barrier encapsulation method

ABSTRACT

The present invention generally relates to organic light emitting diode (OLED) structures and methods for their manufacture. To increase the lifetime of an OLED structure, an encapsulating layer may be deposited over the OLED structure. The encapsulating layer may fully enclose or “encapsulate” the OLED structure. The encapsulating layer may have a substantially planar surface opposite to the interface between the OLED structure and the encapsulating layer. The planar surface permits successive layers to be evenly deposited over the OLED structure. The encapsulating layer reduces any oxygen penetration into the OLED structure and may increase the lifetime of the OLED structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/371,171, filed Feb. 13, 2009 now U.S. Pat. No. 7,951,620 and issuedMay 31, 2011, which claims benefit of U.S. Provisional PatentApplication Ser. No. 61/036,230, filed Mar. 13, 2008. Each of theaforementioned related patent applications is herein incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention generally relate to an organiclight emitting diode (OLED) structure and a method for its manufacture.

2. Description of the Related Art

OLED displays have gained significant interest recently in displayapplications in view of their faster response times, larger viewingangles, higher contrast, lighter weight, lower power, and amenability toflexible substrates, as compared to liquid crystal displays (LCD). Inaddition to organic materials used in OLEDs, many polymer materials arealso developed for small molecule, flexible organic light emitting diode(FOLED) and polymer light emitting diode (PLED) displays. Many of theseorganic and polymer materials are flexible for the fabrication ofcomplex, multi-layer devices on a range of substrates, making them idealfor various transparent multi-color display applications, such as thinflat panel display (FPD), electrically pumped organic laser, and organicoptical amplifier.

The lifetime of display devices can be limited, characterized by adecrease in electroluminescence efficiency and an increase in drivevoltage. The limited lifetime may be due to the degradation of organicor polymer materials and the formation of non-emissive dark spots.Material degradation and dark spot problems may be caused by moistureand oxygen ingress. For example, exposure to humid atmospheres is foundto induce the formation of crystalline structures of 8-hydroxyquinolinealuminum (Alq₃), which is often used as the emissive layer, resulting incathode delamination, and hence, creating non-emissive dark spotsgrowing larger in time. In addition, exposure to air or oxygen may causecathode oxidation. Once organic material reacts with water or oxygen,the organic material is dead.

Therefore, there is a need in the art for an OLED structure that doesnot degrade or form non-emissive dark spots. There is also a need for amethod to produce such a structure.

SUMMARY OF THE INVENTION

The present invention generally relates to OLED structures and methodsfor their manufacture. To increase the lifetime of an OLED structure, anencapsulating layer may be deposited over the OLED structure. Theencapsulating layer may fully enclose or “encapsulate” the OLEDstructure. The encapsulating layer may have a substantially planarsurface opposite to the interface between the OLED structure and theencapsulating layer. The planar surface permits successive layers to beevenly deposited over the OLED structure. The encapsulating layerreduces any oxygen penetration into the OLED structure and may increasethe lifetime of the OLED structure.

In one embodiment, an organic light emitting diode structure comprises asubstrate and an organic light emitting diode portion disposed over thesubstrate. The organic light emitting diode portion may comprise a holetransport layer, an emissive layer, and an encapsulating portion. Theencapsulating portion may comprise an organic layer substantiallyenclosing the organic light emitting diode portion and coupled to boththe organic light emitting diode portion and the substrate. Theencapsulating portion may have a substantially planar surface extendingover the entire organic layer and disposed opposite to an interfacebetween the organic light emitting diode portion and the encapsulatingportion.

In another embodiment, an organic light emitting diode manufacturingmethod comprises depositing an organic light emitting diode layeredstructure over a substrate and depositing an organic encapsulating layerover the organic light emitting diode layered structure and thesubstrate. The organic encapsulating layer may be coupled to both thesubstrate and the organic light emitting diode layered structure. Theorganic encapsulating layer may have a substantially planar surfaceextending across the entire surface opposite to an interface between theorganic light emitting diode layered structure and the organicencapsulating layer.

In another embodiment, an organic light emitting diode manufacturingmethod comprises inkjet depositing an organic encapsulating layer over asubstrate. The substrate having an organic light emitting diode layeredstructure disposed thereon. The encapsulating layer may be coupled toboth the substrate and the organic light emitting diode layeredstructure. The encapsulating layer may have a substantially planarsurface disposed opposite to an interface between the organic lightemitting diode layered structure and the organic encapsulating layer.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 is a schematic perspective view of an apparatus 100 for inkjetprinting according to one embodiment of the invention.

FIG. 2 is an OLED structure 200 according to one embodiment of theinvention.

FIG. 3 is an OLED structure 300 incorporating an encapsulating layer 320according to one embodiment of the invention.

FIG. 4 is an OLED structure 400 incorporating an encapsulating layer 406according to another embodiment of the invention.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation.

DETAILED DESCRIPTION

The present invention generally relates to OLED structures and methodsfor their manufacture. To increase the lifetime of an OLED structure, anencapsulating layer may be deposited over the OLED structure. Theencapsulating layer may fully enclose or “encapsulate” the OLEDstructure. The encapsulating layer may have a substantially planarsurface opposite to the interface between the OLED structure and theencapsulating layer. The planar surface permits successive layers to beevenly deposited over the OLED structure. The encapsulating layerreduces any oxygen penetration into the OLED structure and may increasethe lifetime of the OLED structure.

FIG. 1 is a schematic perspective view of an apparatus 100 for inkjetprinting according to one embodiment of the invention. It is to beunderstood that while two inkjet heads 102, 104, have been shown, moreor less inkjet heads may be present. The apparatus 100 also includes abridge 114 on which the inkjet heads 102, 104, are mounted. The inkjetheads 102, 104 may be spaced apart along the bridge 114 in an arrayfashion such that multiple inkjet heads 102, 104 may be used to deliverorganic encapsulating material to the substrate 118. In one embodiment,the inkjet heads 102, 104 deliver organic encapsulating material todifferent areas of the substrate 118. In another embodiment, the inkjetheads 102, 104 may be coupled together. One or more monitors or cameras116 may be mounted to the bridge 114. The substrate 118 may be disposedon a substrate stage 120. During operation, the substrate stage 120 maymove the substrate 118 under the inkjet heads 102, 104, where inkjetdroplets may be dispensed onto the substrate 118. The monitors orcameras 116 may perform metrology on the droplets as well as on thedeposited material. The inkjet apparatus 100 may be used to deposit manyof the films of an OLED structure.

FIG. 2 is an OLED structure 200 according to one embodiment of theinvention. The structure 200 comprises a substrate 202. In oneembodiment, the substrate 202 is a flexible, roll to roll substrate. Itis to be understood that while the substrate 202 is described as a rollto roll substrate, other substrates may be utilized to produce OLEDsincluding soda lime glass substrates, silicon substrates, semiconductorwafers, polygonal substrates, large area substrates, and flat paneldisplay substrates.

Over the substrate 202, an anode 204 may be deposited. In oneembodiment, the anode 204 may comprise a metal such as chromium, copper,or aluminum. In another embodiment, the anode 204 may comprise atransparent material such as zinc oxide, indium-tin oxide, etc. Theanode 204 may have a thickness between about 200 Angstroms and about2000 Angstroms.

A hole injection layer 206 may then be deposited over the anode 204. Thehole injection layer 206 may have a thickness between about 200Angstroms and about 2000 Angstroms. In one embodiment, the holeinjection layer 206 may comprise a material having a straight chainoligomer having a phenylenediamine structure. In another embodiment, thehole injection layer 206 may comprise a material having a branched chainoligomer having a phenylenediamine structure.

A hole transport layer 208 may be deposited over the hole injectionlayer 206. The hole transport layer 208 may have a thickness betweenabout 200 Angstroms to about 1000 Angstroms. The hole transport layer208 may comprise a diamine. In one embodiment, the hole transport layer208 comprises a naphthyl-substituted benzidine (NPB) derivative. Inanother embodiment, the hole transport layer 108 comprises N,N′-diphenyl-N, N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine(TPD).

An emissive layer 210 may be deposited over the hole transport layer208. The emissive layer 210 may be deposited to a thickness betweenabout 200 Angstroms to about 1500 Angstroms. Materials for the emissivelayer 210 typically belong to a class of fluorescent metal chelatedcomplexes. In one embodiment, the emissive layer comprises8-hydroxyquinoline aluminum (Alq₃).

An electron transport layer 212 may be deposited over the emissive layer210. The electron transport layer 212 may comprise metal chelatedoxinoid compounds. In one embodiment, the electron transport layer 212may comprise chelates of oxine itself (also commonly referred to as8-quinolinol or 8-hydroxyquinoline). The electron transport layer 212may have a thickness between about 200 Angstroms to about 1000Angstroms.

An electron injection layer 214 may be deposited over the electrontransport layer 212. The electron injection layer 214 may have athickness between about 200 Angstroms to about 1000 Angstroms. Theelectron injection layer 214 may comprise a mixture of aluminum and atleast one alkali halide or at least one alkaline earth halide. Thealkali halides may be selected from the group consisting of lithiumfluoride, sodium fluoride, potassium fluoride, rubidium fluoride, andcesium fluoride, and suitable alkaline earth halides are magnesiumfluoride, calcium fluoride, strontium fluoride, and barium fluoride.

A cathode 216 may be deposited over the electron injection layer 214.The cathode 216 may comprise a metal, a mixture of metals, or an alloyof metals. In one embodiment, the cathode 216 may comprise an alloy ofmagnesium (Mg), silver (Ag), and aluminum (Al). The cathode 216 may havea thickness between about 1000 Angstroms and about 3000 Angstroms. Anelectrical bias may be supplied to the OLED structure 200 by a powersource 218 such that light will be emitted and viewable through thesubstrate 202. The organic layers of the OLED structure 200 comprise thehole injection layer 206, the hole transport layer 208, the emissivelayer 210, the electron transport layer 212, and the electron injectionlayer 214. It should be noted that not all five layers of organic layersare needed to build an OLED structure. For example, in some cases, onlythe hole transport layer 208 and the emissive layer 210 are needed.

FIG. 3 is an OLED structure 300 incorporating an encapsulating layer 320according to one embodiment of the invention. The OLED structure 300includes a substrate 302, anode 304, hole injection layer 306, holetransport layer 308, emissive layer 310, electron transport layer 312,electron injection layer 314, and a cathode 316. The OLED structure 300may be connected to a power source 318. An encapsulating layer 320 maybe deposited on the OLED structure 300. The encapsulating layer 320 mayhave a surface 322 that is substantially planar. The surface 322 may bedisposed opposite to the interface between the encapsulating layer 320and the cathode 316. It is to be understood that while five layers oforganic layers are shown for the OLED structure 300, all five layers arenot needed to build the OLED structure 300.

The encapsulating layer 320 may have a thickness between about 4 micronsand about 6 microns. The encapsulating layer 320 may be deposited byinkjetting. In one embodiment, the encapsulating layer may comprise amixture of an acrylate, a methacrylate, and acrylic acid. In oneembodiment, the acrylate may comprise between about 25 volume percent toabout 50 volume percent of the total mixture. In another embodiment, theacrylate may comprise between about 30 volume percent and about 40volume percent of the total mixture.

The methacrylate may be present in an amount between about 10 volumepercent and about 25 volume percent of the total mixture. In oneembodiment, the methacrylate may be present in an amount between about15 volume percent and about 20 volume percent of the total mixture. Theacrylic acid may be present in an amount between about 2 volume percentand about 20 volume percent of the total mixture. In one embodiment, theacrylic acid may be present in an amount between about 2.5 volumepercent and about 10 volume percent of the total mixture. Of course, itis to be understood that additional additives may be utilized to depositthe encapsulating layer 320.

The encapsulating layer 320 covers any defects that may be present onthe OLED structure 300. The encapsulating layer 320 seals the defects.Additionally, the encapsulating layer 320 covers any particles that maybe present on the OLED structure 300 and seals the particles under theencapsulating layer 320. Any voids that may be present on the OLEDstructure 300 may be covered and sealed by the encapsulating layer 320also.

The encapsulating layer 320 may be deposited onto the OLED structure 320and then planarized so that the uppermost surface 322 of theencapsulating layer 320 is substantially planar. The substantiallyplanar surface 322 of the encapsulating layer 320 eliminates stepcoverage concern for any layers deposited after the encapsulating layer320. Any layers deposited over the encapsulating layer 320 may thus bedeposited to a uniform thickness over not just the OLED structure 200,but the entire device of which the OLED is a part.

FIG. 4 is an OLED structure 400 incorporating an encapsulating layer 406according to another embodiment of the invention. The OLED structure 400comprises a substrate 402 having an OLED portion 404 deposited thereon.An organic encapsulating layer 406 may be deposited over the OLEDportion 404 and the substrate 402. After deposition, the encapsulatinglayer 406 may be planarized such that the surface opposite to theinterface with the OLED portion 404 may be substantially planar. Theencapsulating layer 406 will thus have a thin portion as shown by arrow“A” over the OLED portion 404 and a thicker portion, relative to thethin portion, as shown by arrow “B” over just the substrate 402.

Above the encapsulating layer 406, a multi-layer water-barrierencapsulation structure may be deposited to a thickness as shown byarrow “C”. The first layer 408 deposited on the encapsulating layer 406may comprise silicon and be deposited to a thickness shown by arrow “D”.In one embodiment, the first layer 408 may comprise silicon nitride. Inone embodiment, the first layer 408 may be between about 0.1 microns toabout 0.6 microns thick.

The second layer 410 may be deposited over the first layer 408. Thesecond layer 410 may comprise carbon. In one embodiment, the secondlayer 410 may have a thickness as shown by arrow “E” of between about0.1 microns and about 0.6 microns. A third layer 412 may be depositedover the second layer 410. The third layer 412 may be deposited to athickness as shown by arrow “F”. In one embodiment, the thickness of thethird layer 412 may be between about 0.1 microns and about 0.6 microns.The third layer 412 may comprise silicon. In one embodiment, the thirdlayer 412 may comprise silicon nitride.

A fourth layer 414 may be deposited over the third layer 412. The fourthlayer 414 may comprise carbon. In one embodiment, the fourth layer 414may have a thickness as shown by arrow “G” of between about 0.1 micronsand about 0.6 microns. A fifth layer 416 may be deposited over thefourth layer 414. The fifth layer 416 may be deposited to a thickness asshown by arrow “H”. In one embodiment, the thickness of the fifth layer416 may be between about 0.1 microns and about 0.6 microns. The fifthlayer 416 may comprise silicon. In one embodiment, the fifth layer 416may comprise silicon nitride.

Each layer of the multi-layer water-barrier encapsulation structure mayhave substantially the same thickness. The presence of the encapsulatinglayer 406 provides an additional water-barrier and permits themulti-layer water-barrier encapsulation structure to be thinner ascompared to the situation where the encapsulating layer 406 is notpresent. In the absence of the encapsulating layer 406, the first layer408, the second layer 410, the third layer 412, the fourth layer 414,and the fifth layer 416 may each have a thickness between about 3microns and about 6 microns. The multi-layer water-barrier encapsulationstructure may be thinner because it does not have to cover defects,particles or voids in the OLED portion 404.

Thus, by depositing an organic encapsulating layer over an OLEDstructure, defects, particles, and voids of the OLED structure may becovered and sealed. The encapsulating layer may be planarized afterdeposition. The planar surface allows subsequently deposited layers tohave a uniform thickness over the entire device and not just the OLEDstructure due to the lack of step coverage for the subsequent layers.The encapsulating layer, by covering and sealing the OLED structure andthe particles, voids, and defects, may reduce dark spot formation andOLED structure degradation.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

The invention claimed is:
 1. An organic light emitting diodemanufacturing method, comprising: depositing an organic light emittingdiode layered structure over a substrate; and depositing a multi-layerwater-barrier encapsulation structure over the organic light emittingdiode layered structure, the encapsulating water-barrier encapsulationstructure comprising one or more layers comprising silicon and one ormore layers comprising carbon, wherein each layer of the multi-layerwater barrier encapsulation structure has the same thickness.
 2. Themethod of claim 1, wherein the one or more layers comprising carboncomprises a mixture of an acrylate, a methacrylate, and acrylic acid. 3.The method of claim 2, wherein the acrylate comprises about 25 volumepercent to about 50 volume percent.
 4. The method of claim 2, whereinthe methacrylate comprises about 10 volume percent to about 25 volumepercent.
 5. The method of claim 1, further comprising: depositing theone or more layers comprising silicon over the organic light emittingdiode layered structure; and depositing the one or more layerscomprising carbon over the one or more layers comprising silicon.
 6. Themethod of claim 5, wherein the one or more layers comprising siliconcomprise silicon nitride.
 7. The method of claim 1, wherein the one ormore layers comprising silicon comprise silicon nitride.
 8. An organiclight emitting diode structure, comprising: a substrate; an organiclight emitting diode portion disposed over the substrate; and amulti-layer water-barrier encapsulation structure disposed over theorganic light emitting diode portion, the water-barrier encapsulationstructure comprising one or more layers comprising silicon and one ormore layers comprising carbon, wherein each layer of the multi-layerwater barrier encapsulation structure has the same thickness.
 9. Thestructure of claim 8, wherein the organic light emitting diode portioncomprises: a transparent anode layer; a hole-injection layer disposedover the transparent anode layer; the hole transport layer disposed overthe hole-injection layer; the emissive layer disposed over the holetransport layer; an electron injection layer disposed over the emissivelayer; and a cathode layer disposed over the electron injection layer.10. The structure of claim 8, wherein the one or more layers comprisingcarbon is disposed over the one or more layers comprising silicon. 11.The structure of claim 10, wherein the one or more layers comprisingsilicon comprise silicon nitride.
 12. The structure of claim 11, whereinthe one or more layers comprising silicon and the one or more layerscomprising carbon are disposed over the organic light emitting diodeportion in alternating fashion.
 13. The structure of claim 11, whereinthe one or more layers comprising silicon and the one or more layerscomprising carbon each individually have a thickness between about 0.1microns to about 0.6 microns.
 14. The structure of claim 11, wherein theone or more layers comprising silicon and the one or more layerscomprising carbon collectively have a thickness between about 3 micronsand about 6 microns.
 15. The structure of claim 1, wherein the one ormore layers comprising silicon comprise silicon nitride.